The present invention relates to a consumable electrode gas shielded arc welding method and apparatus. More particularly, the present invention relates to a consumable electrode gas shielded arc welding method and apparatus, which realize appropriate arc heat input density distributions in a groove of a base metal and preserve satisfactory toughness of a weld metal.
In order to prevent weld defects, such as lack of fusion at a bottom of a groove or formation of convex beads in the groove during root running or multi-layer welding of a very narrow groove of a metal joint, which groove has a V or Y shape and a groove angle of about 30xc2x0 or an I or U shape and a clearance of about 5 mm, it is necessary to realize an effective arc heat input density distribution.
A consumable electrode gas shielded arc welding method, which is excellent in efficiency because wide throat thickness is obtained by a single operation, is not exceptional. Strong arc power that can melt a bottom of a groove against an excessively heavy gravity head of molten metal is needed, and large electric current is demanded.
MIG welding, which uses as a shielding gas an inert gas such as argon, or a mixed gas in which an oxidizing gas such as O2 from 2 to 5% or CO2 of less than 20% is a main ingredient and is added to an inert gas, cannot afford such requirements. This is so because the MIG welding basically is concerned with current savings and heat input savings and because a condition range which realizes free defect welding of a bottom of a groove is narrow.
On the other hand, the MIG welding is very effective for beads. Stable and fine melting is indispensable for preserving a wetting property at a toe of the beads. A cathode cleaning action of the MIG welding, which is remarkably confirmed for a wide range of the shielding gas, is also effective for stable and fine melting of the toe.
MAG welding which uses an oxidizing gas usually uses Ar+20% CO2 for a shielding gas, and its condition range for which free defect welding at a bottom of a groove is realized is very narrow. Consequently, CO2 welding which uses 100% CO2 is demanded.
With the use of an oxidizing shielding gas, it is, however, known that toughness of weld metal is deteriorated. Because of this, decrease of a mixing ratio of the oxidizing gas such as O2 and CO2 is required for preserving sufficient toughness of the weld metal.
The present invention has an object to provide a consumable electrode gas shielded arc welding method and apparatus, which realize appropriate arc heat input density distributions in a groove of a base metal and preserve satisfactory toughness of a weld metal.
This and other objects, features and advantages of the invention will become more apparent upon a reading of the following detailed specification and drawings, in which: